Variable core tuning inductor



Nov. 9, 1965 G, E. GEE ETAL VARIABLE CORE TUNING INDUCTOR Filed June 18,1962 INVENTORSI 2f E fj@ (2C zdd/ 30 60 so 12o .x50 fao 220 E56/P555/Pamr/a/v United States Patent O 3,217,277 VARIABLE CORE TUNING INDUCTORGordon E. Gee and Ray B. Schrecongost, Park Ridge, Ill., assignors toHammond Organ Company, Chicago, Ill., a corporation of Delaware FiledJune 18, 1962, Ser. No. 203,271 1 Claim. (Cl. 336-135) This inventionrelates in general to variable core inductors and more particularlyrelates to an audio frequency ferrite core inductor which is tuned byrotational movement to provide a comparatively linear change infrequency for use in tuning organ oscillators.

One typical previous practice for deriving an audio frequency tone in anorgan oscillator involved the use of an iron core tuning inductor. Theinductor comprised a core of stacked laminations which waslongitudinally reciprocated to vary the gap in the magnetic circuit andtherefore the nominal frequency of the associated oscillator. Thisarrangement was somewhat diicult to adjust precisely, and in addition,since a number of such inductors were mounted in adjacent positions,considerable magnetic interaction might occur unless special preventivetechniques were used. The difficulty in adjusting or tuning an inductorof the type described is that its reactance varies in such a manner thatminute changes in the air gap result in great changes in oscillatorfrequency so that precise tuning is diicult to achieve while anysubsequent slight misalignment results in a considerable variance in theouto put frequency from what is desired.

Another type of widely used tuning inductor incorporates a so-calledferrite core and cap, with the core being cup-shaped and having a centerpost about which the coil is mounted. The center post projects towardthe cap which is rotatable. The cap is provided with a D-shaped recess,and the post is provided with a similarly shaped portion so that whenthe cap is rotated, the area of the gap therebtween is altered to varythe frequency of the associated oscillator. This arrangement, however,is subject to wide fluctuations in the amount of frequency variation perincrement of rotation of the cap if a substantial percentage range oftuning is to be provided. Thus if a large over all change in frequencyis to be provided, the cap must be rotated over an arc which brings theedge of the cap recess into proximity with an edge on the core,resulting in considerable flux leakage and local saturation so that thefrequency may change very abruptly in response to slight movement of thecap.

It is therefore an object of the present invention to provide a variablereluctance inductor which may be rotatably adjusted to provide linearpercentage frequency changes in the output of an associated oscillator.

It is another object of the present invention to provide a variablereluctance inductor utilizing a rotatable cap element for adjustment,which may be rotated over a considerable arc to provide a large linearchange in frequency while at the same time the sensitivity of theinductor is reduced to the point where incremental movement of the capdoes not give rise to a large percentage shift in frequency.

Briefly, the objects of the present invention are accomplished byproviding a ferrite cup having a center post or core with the coilcarried between the core and cup wall. The core has a predeterminedshape formed at one end and cooperates with a rotatable ferrite capelement having another predetermined shape formed therein to provide asubstantially linear change in the output frequency of the associatedoscillator when the cap is rotated relative to the core. Thus theinductive effect is controlled by rotatably varying the area of closeproximity between opposing surfaces of the core and cap in such a mannerlee that edge areas are not alone maintained in close coupledrelationship.

In the drawings:

FIG. 1 is a cross sectional view of one embodiment of the inductorillustrating the relationship between the tuning cup and cap;

FIG. 2 is a front elevational view of the tuning cup;

FIG. 3 is a front elevational view of the cap;

FIG. 4 illustrates another embodiment of the cap;

FIG. 5 is a graph illustrating percentage frequency shifts for variouspositions of the cap relative to the cup shown in FIG. l; and

FIG. 6 is a graph illustrating percentage frequency shifts for variouspositions of the cap shown in FIG. 4.

In FIG. l a variable tuning core inductor incorporating the principlesof the invention is illustrated by the reference character 10. Itcomprises a ferrite cup 12 having a center post or core 14 projectingfrom a back wall 16, and a pair of spaced apart semicircularly shapedwalls 18 separated at their edges by narrow slots 50 which areconvenient for passing leads to the coil 22 and coaxial with post 14. Abobbin havin a coil 22 is seated in the cup between the core 14 and thewalls 18.

An aperture or passageway 24 is provided in the center post 14 and backwall 16 for the purpose of enabling the generally circular tuning cap 26having a central aperture 28 to be rotatably mounted on the cup. The cap26 is normally engaged flush with the walls 18 and is shown separatedtherefrom in FIG. l primarily for the purpose of clarity. The coil 22 isthus maintained in a substantially completely shielded environmentwhereby coupling between adjacent inductors is substantially minimized.

It will be noted that the center post 14 does not extend as far from theback wall 16 as do the walls 18 so that there is a slight air gapbetween the post 14 and cap 26 to thereby minimize the interactiontherebetween and reduce the sensitivity of the assembly. In addition,the center post is provided with a recess or cut away portion 30 definedby the peripheral wall 32 of the center post and a circular wall 34whose radius extends from the axis passing through point 38 offset fromthe axis of the center post, as seen in FIG. 2.

The cap 26 is also provided with a recess 40. This recess 40 is crescentshaped and formed by a pair of intersecting radial walls 42 and 44, withwall 42 having its axis of rotation coaxial with the aperture 28 and thewall 44 having its axis offset therefrom as shown by point 46 concentricwith point 38. Both of these points lie on a plane passing through adiameter of the cap and core.

In assembling the cup 12 and cap 26 for use, the slots on spacingbetween cup walls 18 and a pair of spaced apart recesses 51 in the edgeof cap 26 are used to align the cap so that a line from point 46bisecting the recess 40 is aligned at 90 to a similar line bisectingrecess 30. This position should normally result in the reluctance of theair gap between the cup and cap being such that the inductance is tunedto a desired audio frequency to be supplied in an organ with thefrequency being dependent on the parameters of the coil. However, itoften happens that the tolerance of the various components has beenexceeded or that characteristics may vary. It therefore becomesnecessary to adjust the relative position of the cap and cup so that therelationship between the recesses is changed.

FIG. 5 illustrates characteristic percentage shifts in frequency in theapproximate ranges of Z50-450, 500- 825, and 1300-1500 cycles when thecap is rotated relative to the core. From to 60 approximately a 5%linear shift in frequency occurs, while from 90 to 120 a similar linearpercentage shift in frequency occurs in the other direction. The 90 axiscorresponds to the described assembled relationship between recesses 30and 40 so that rotation of the cap in either direction from theassembled position will provide slight linear changes in frequencythereby permitting facile adjustment.

FIG. 4 illustrates another cap 52. The cap 52 is similar to cap 26except that a D-shaped recess 54 is provided therein. The straight legof the D lies adjacent or parallel to the diameter of the cap, and theradial leg of the recess 54 is coaxial with the center of the cap.

The arrangement shown in FIG. 4 is assembled to the cup 12 in the samemanner as described for cap 26 with a line bisecting the straight leg ofthe D lying at 90 to a line bisecting recess 30. This corresponds to the90 line indicated by the graph in FIG. 6, and it Will be noted thatrotation in either direction results in a substantially linearpercentage shift in frequency for frequencies between approximately1400-1800 cycles as shown in FIG. 5, but with a higher slope.

Thus, having described our invention, but believing the same capable ofnumerous modifications and adaptations, there is appended hereto a claimwhich is believed to incorporate the inventive concept.

We claim:

A variable inductor comprising a one piece ferrite cup providing an endwall, a cylindrical post extending upwardly from the end wall, side Wallstructure extending upwardly from the end Wall concentric with the postto provide an annular space between the post and the side Wallstructure, a coil in said annular space surrounding the post, the upperedge of the side wall structure being at and the upper end of the posthaving a Hat surface generally parallel to the side wall flat surface, aferrite cap having a Hat lower face engaging substantially the entireflat upper edge of the side wall structure and overlying the post end,the end of the cylindrical post and the juxtaposed central portion ofthe cap when the cup and cap are together in alignment forming a pair ofopposed generally circular regions, the cap within said region having aD shaped recess having a convex edge occupying substantially half thecircular region and the post end having a crescent shaped recess havinga convex edge at one side, the convex edge of the crescent shaped recesshaving the same radius of curvature as the post cylindrical surface, andthe convex edges of both recesses having a common center of curvaturewhich is substantially at the common axis of the cup and cap, said capbeing rotatable relative to said cup to overlap said recesses to agreater 0r lesser extent.

References Cited by the Examiner UNITED STATES PATENTS JOI-IN F. BURNS,Primary Examiner.

